Endothelium-dependent and endothelium-independent flow regulation in coronary vascular regions supplied by arterial and venous bypass grafts.

The endothelium-dependent and endothelium-independent vasodilation of arterial and venous coronary bypass grafts and of epicardial conduit vessels and microcirculatory coronary vessels supplied by these grafts was investigated. Vasodilatory response and flow regulation were tested with cumulative intracoronary doses of acetylcholine (25 and 50 micrograms i.c.), nitroglycerin (0.3 mg i.c.), and papaverine (10 mg i.c.) in 10 patients (age 60 +/- 2.3 years) with arterial grafts and in 16 patients (age 57.7 +/- 1.5 years) with venous grafts. The effect of acetylcholine on arterial and venous bypass grafts and on large conduit arteries was evaluated by quantitative coronary angiography. Coronary blood flow velocity changes as a parameter of microcirculatory function were measured by intraluminal Doppler ultrasound. Indices for coronary flow and coronary resistance were calculated from the mean Doppler flow velocity and the computed cross-sectional vascular area. The coronary resistance decreased endothelium dependent after 25 and 50 micrograms of acetylcholine by 16 +/- 30% (p < 0.05 vs. control) and 22 +/- 25% (p < 0.05 vs. control), respectively, in regions supplied by venous grafts and by 48 +/- 20% (p < 0.05 vs. control and vs. venous graft) and 41 +/- 32% (p < 0.05 vs. control), respectively, in regions supplied by arterial grafts. The coronary resistance decreased endothelium independent after 0.3 mg nitroglycerin and 10 mg papaverine by 18 +/- 56% (p < 0.05 vs. control) and 39 +/- 29% (p < 0.05 vs. control), respectively in regions supplied by venous grafts and by 45 +/- 45% (p < 0.05 vs. control) and 70 +/- 12% (p < 0.05 vs. control and vs. venous graft), respectively in regions supplied by arterial grafts. In conclusion, during the long-term course after coronary artery bypass grafting, vascular regions supplied by arterial grafts have a better preserved endothelium-dependent and endothelium-independent flow reserve as compared with vascular regions supplied by venous grafts.